3G vs. 3GS Sim cards are they interchangable?

I have an Iphone 3G 16 gig and want to upgrade to the 3G S with 32 gigs(16 just doesnt cut it). Since I bought the Iphone in October, At&t wont let me get the subsidy pricing until February 2010. My father has a separate at&t account and suggested that he take my iphone off my hands and allow me to buy, the 3gs using his acct and just switch out the sim cards. Im trying to figure out if it is as simple as this. Does the 3GS use the same type of sim card as the 3G? Is there a difference in the plan types? From what I can tell both the phones require the standard unlimited data plan. Will there be any data plan change for the HSPDA? Would At&t have some problem with me doing that?

I do not about the SIM card from the iPhone 3G, but I am using in my new 3G S the SIM card from my original (2007) iPhone. Seriously, SIM cards are standard. They are not tied to any specific make or model cell phone. Your SIM card from your 3G will work just fine in your new 3G S.

I have an Iphone 3G 16 gig and want to upgrade to the 3G S with 32 gigs(16 just doesnt cut it). Since I bought the Iphone in October, At&t wont let me get the subsidy pricing until February 2010. My father has a separate at&t account and suggested that he take my iphone off my hands and allow me to buy, the 3gs using his acct and just switch out the sim cards. Im trying to figure out if it is as simple as this. Does the 3GS use the same type of sim card as the 3G? Is there a difference in the plan types? From what I can tell both the phones require the standard unlimited data plan. Will there be any data plan change for the HSPDA? Would At&t have some problem with me doing that?

They're absolutely interchangeable. My wife qualified for the upgrade while I did not (though we are on a family plan). I used her line to order at the discounted price; activated the phone on her account, and then swapped SIMS and did a restore on each phone from our appropriate backups (to get my mail/settings on the new phone). Now I have a shiny new 3GS and she has my shiny old 3G.

I do not about the SIM card from the iPhone 3G, but I am using in my new 3G S the SIM card from my original (2007) iPhone. Seriously, SIM cards are standard. They are not tied to any specific make or model cell phone. Your SIM card from your 3G will work just fine in your new 3G S.

Only if you have the Data plan on both phones already.. What is stored on them is the ATT info..

Not sure how you are using an edge sim in an 3g phone.. I would maybe want to go get a 3g card they have different ones.. (not sure how this effects the speed or network..